HVLP off a SCUBA tank?

I looked at HVLP sprayers on eBay and clearly the price of a system seems to be in the air handling, not the sprayer/cup assembly. Has anyone tried it or does it sound like it would work if the right regulator could be put together?

(post #109372, reply #1 of 15)

I've used high pressure air tanks to power nail guns, but I'm not so sure they contain enough air volume to spray even small projects. HVLP requires a LOT of air. When volunteer fireman, I used 1800-psi breathing apparatus (BA) tanks to power "Jaws of Life" cutting tools, as well as other emergency equipment. The relatively small bottles have a regulator that delivers controllable pressures up to 120-psi, and they're usually equipped with a backpack and 6-foot hose with a quick connect fitting for tools. It can't be beat for trimming, because it contains enough volume to work all day without making noise or having to drag around lots of hose. Nail guns, however, require far less air than spray equipment. And where an 1800 to 2600-psi BA tank is relatively small and portable, I think a 3500-psi SCUBA tank is only back-packable when I'm under water. I wouldn't want to manuver one around the shop or job site while while trying to produce a quality finish. Finally, unless you're a licensed SCUBA diver or a firefighter, you'll have difficulty refilling your tank.

All that said, I've gotta say that it might be worth a try. So let us know if you do.

(post #109372, reply #2 of 15)

I cannot think of anything more dangerous than using compressed gas tanks to power sprayers and nailers. If the regulator fails or malfunctions, the tool you would be holding could become a bomb and literally explode in your hand.

I wrote an Extension Publication on Pneumatic Nailers. During that research, I read through most manufacturer's literature and I believe all the manufacturers recommended that their tools never be hooked up to high pressure tanks. If you use a gas like oxygen, any spark, like the driver striking the nail, could cause the oxygen to ignite.

There are reasonably priced air compressors for spraying that are a worthwhile investment. To cobble something together with the hope of saying a few bucks is "penny-wise, pound-foolish" thinking.

(post #109372, reply #3 of 15)

SCUBA and BA tanks don't contain pure oxygen, they're filled with air, the same mix you're breathing as you read this. Think about it: neither a firefighter or diver can breath pure oxygen. A firefighter certainly wouldn't bring pure oxygen into a burning structure! Secondly, high pressure air tanks have powered firefighting and scuba tools for a long time, and its dangerous to misuse or abuse any tool, such as a high pressure air tank or its regulator, as well as a standard small shop compressor. We all should know the danger of rusted compressor tanks.

To use or have a high pressure air tank filled, you've gotta be a licensed and current SCUBA diver or a firefighter. Either way, one would have to learn about and maintain a high respect for the equipment. Your caution should be heeded, but I think you're being just a little too paranoid.

(post #109372, reply #4 of 15)

There are a couble of risks here. One is a literal bomb, high pressure air with combustible finish. I suspect that compressed air is not a great deal less dangerous than pure oxygen in that regard. Using a waterborne finish will eliminate this possibility.

Another is just overpressure. Having your paint pot blow up in your hand would feel very like a bomb even if the pressurizing gas was something entirely inert, like argon. A pressure relief valve just downstream from the regulator should take care of it. Or two if you're feeling particularly paranoid.

(post #109372, reply #5 of 15)

I guess what I am really asking is: "How feasible is it to rig a regulator between a SCUBA tank and a HLVP gun? Both spraying and breathing off scuba have very similar needs: stead flows of air, on demand. The "on-demand" part is the tricky bit: in SCUBA, the regulation of air occurs in two phases: at the tank and at the mouthpiece, hence the name "two-stage regulator". I have no experience in HLVP pneumatics, but the need seems to be the same. I should figure out how a gun and its compressor work first, but it can't be that complicated in principle. Cousteau figured it out as a teenager one summer in Lake Champlain in VT, working out of his garage with a buddy...

(post #109372, reply #6 of 15)

I don't see a problem other than volume. Not being a SCUBA guy, I'd look into a nitrogen tank and a good welding regulator. I used to use a 3000# Q-bottle of nitrogen and a high-precision regulator to calibrate pressure transmitters and switches in petro-chem plants. Way better than a dead weight tester.

John O'Connell - JKO Handcrafted Woodworking

Life is tough. It's tougher if you're stupid - John Wayne

John O'Connell - JKO Handcrafted Woodworking

The more things change ...

We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.

(post #109372, reply #8 of 15)

When I started diving, the tanks were galvanized & held 72 cu.ft. at 2250 psi. The newer aluminum tanks held 80 cu.ft. at 3000 psi. Assuming you have a tank & can find a regulator that will fit the valve that is unique to scuba I believe that if you work out the cfm requirements for whatever use you are making and factor in the cost of refilling the tank, you will find a compressor to still be the less expensive option.

(post #109372, reply #9 of 15)

I have to ask what systems you're looking at that the gun price versus air supply price are so out of whack....I've seen half-way decent HVLP conversion guns (which is what your talking about, right?) starting at say $250 up to about $800, so depending on the gun model, you might be a lot better off, as one poster suggested, getting a less expensive compressor (if you want to go conversion). Also, you didn't say what you wanted to do...if woodworking or auto work or something else is leading you down the HVLP path, then it might make sense to start thinking about the compressor to run other tools you might use at a later date.

(post #109372, reply #11 of 15)

If I remember correctly, a scuba cylinder's stated volume is actually an equivalent volume based on atmospheric pressure. So an 80 cu.ft. tank (usually closer to 77) will last less than 10 minutes with a gun requiring 7.5 cfm, depending on the pressure drop required at the nozzle, length of the hose, etc.

I don't see that it would be more dangerous than a compressor, assuming that it is maintained and inspected like a typical scuba setup, but as someone said, you would probably need to be certified to get it refilled. Kind of a neat idea, but I don't think it's too practical unless your spray sessions are very brief and very infrequent.

(post #109372, reply #12 of 15)

While I've two tanks and can get the air, it clearly seems that the compressor is the way to go. A fill costs about $5 minimum, plus time and trouble. At $5/10 spraying minutes/tank, that's just 40 hours of spraying for a $200 compressor. As I will likely move all finishing to HVLP, it makes sense to get a compressor.

(post #109372, reply #13 of 15)

I have a 4hp/30gal/11cfm @ 90psi compressor and a very good conventional Binks #95 gun. I am very seriously considering switching over to a LVLP conversion gun. On the other hand my buddy swears by his turbine set-up and watching him spray a few times has really impressed me - no overspray and most importantly, absolutely constant delivery pressure/pattern control. He uses mostly Enduro Poly. I will be borrowing his set-up in a few weeks to spray 14 High-back Stickley chairs I'm building for him. If his new non-metallic gun lives half-way up to his claims it'll be clinched for sure. I'll probably build the turbine housing myself as he did. They have replacement turbines at Graingers. If I can put it all together for $500, a 50% min. improvement in transfer efficiency will save $27.50 per gal of finish at $55 gal. The new set-up will pay for itself in 18.2 gals, even ignoring labor and energy savings.

Whatever you do don't make the same mistake I did. Don't be cheap and buy an oil-less compressor. They are obnoxiously noisey and as they wear the CFM numbers start to fall. I won't be disappointed when mine gives up the ghost. If you're going to get a compressor just for spraying, don't. Go turbine. Conversion guns just aren't as good or efficient or so I'm told. If you want a good convential gun despite the limitations let me know, I'll make you a deal.

John O'Connell - JKO Handcrafted Woodworking

Life is tough. It's tougher if you're stupid - John Wayne

John O'Connell - JKO Handcrafted Woodworking

The more things change ...

We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.